1. Technical Field of the Invention
The present invention relates to a gas sensor for detecting a concentration of specified gas in gas to be measured.
2. Description of the Related Art
In related art, it has been a common practice for an internal combustion engine of a motor vehicle to have an exhaust system on which a gas sensor is mounted for measuring a concentration of specified gas such as oxygen or nitrogen oxide contained in exhaust gases.
One example of such a gas sensor is disclosed in Japanese Unexamined Patent Publication No. 2003-294684. Such a related art gas sensor is shown in FIGS. 14 to 17. As shown in FIG. 14, a gas sensor 9 comprises a sensor element 92, composed of a plate-like bar, which has a detecting section for detecting a concentration of specified gas in measuring gas, which is inserted to and supported with an element-side insulator 93. The element-side insulator 93 is disposed in and supported with a housing 94. The sensor element 92 has an upper base end that is covered with an atmosphere-side insulator 95 placed in axial alignment with the element-side insulator 93. Further, the housing 94 has a base end that fixedly supports an atmosphere-side cover 96 with which the atmosphere-side insulator 95 is covered.
The upper base end of the sensor element 92 has opposing surfaces formed with electrode terminals 921 electrically connected to the detecting section. The atmosphere-side insulator 95 internally accommodates a plurality of spring terminals 972 held in electrical contact with the electrode terminals 921 of the sensor element 92 to provide electrical connection between the electrode terminals 921 and lead wires 971. With such a structure, mounting the atmosphere-side insulator 95 on the base end portion of the sensor element 92 so as to cover the same allows the spring terminals 972 to be brought into pressured contact with the electrode terminals 921 of the sensor element 92.
With the structure set forth above, the sensor element 92 is apt to be held with an element holder 934, composed of the housing 94 and the element side insulator 93, under a tilted condition with respect to an axial direction of the element holder 934. Under such a situation, as shown in FIG. 15, if an attempt is made to locate the atmosphere-side insulator 95 on an upper surface of the element holder 934 with an end face 951 of the atmosphere-side insulator 95 held in contact with a base end face 935 of the element holder 934, a deterioration occurs in a positional relationship between the spring terminals 972, accommodated in an inside of the atmosphere-side insulator 95, and the electrode terminals 921 of the sensor element 92. This results in defective electrical contact between the spring terminals 972 and the electrode terminals 921 of the sensor element 92.
Further, with a requirement for the sensor element 92 to be miniaturized in structure, the sensor element 92 needs to have a narrowed width. With such a structure of the sensor element 92, the electrode terminals 921 also need to have extremely narrowed widths. Thus, the narrower the widths of the electrode terminals 921 formed on the sensor element 92, the more frequent will be for the occurrence of defective electrical contact between the spring terminals 972 and the electrode terminals 921 of the sensor element 92.
With a view to addressing such an issue, it is conceivable for the atmosphere-side insulator 95 to be formed with an inner wall 95a decreased in diameter providing a narrowed clearance 95b between the inner bore 95a of the atmosphere-side insulator 95 and an outer periphery of the sensor element 92 as shown in FIG. 16. With such a structure, however, if the atmosphere-side insulator 95 is placed in a position with reference to the upper end face of the element holder 934 with the sensor element 92 supported in a condition tilted to the element holder 934, a risk liable to occur between the base end of the sensor element 92 and the inner wall 95a of the atmosphere-side insulator 95. This results in a risk of causing damage to the sensor element 92.
With a view to avoiding such an issue, it is also conceivable for the atmosphere-side insulator 95 to be placed with reference to the sensor element 92 in place of the element holder 934 for ensuring correct electrical conductance between the electrode terminals 921 and the spring terminals 972 while avoiding the interference between the sensor element 92 and the atmosphere-side insulator 95 as shown in FIG. 17. With such a structure, an attempt is made to cause an axis of the sensor element 92 and an axis of the atmosphere-side insulator 95 to be aligned with each other even with the sensor element 92 fixed in a condition tilted to the element holder 934 under which the atmosphere-side insulator 95 remains floating from the element holder 934.
However, with the sensor element 92 fixed in the condition tilted to the element holder 934, the atmosphere-side insulator 95 becomes unstable in structure. Under such a circumstance, a risk occurs for a corner area 952 of the end face 951 of the atmosphere-side insulator 95 to conflict the element holder 934, causing damage to the electrode terminals 921 of the sensor element 92.